1. Technical Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and specifically, to an image forming apparatus having a toner cleaner for removing toner attached onto an image carrier such as a photoconductor, a transfer body, or an intermediate transfer body, and an image forming method therefor.
2. Related Art
In an electrophotographic image forming apparatus, development is performed using a developer such as toner. By a developing unit, a toner image is formed for an electrostatic latent image formed on a surface of a photoconductor. The toner image is transferred onto recording paper supplied from a paper feed tray or the like by a transfer unit. The toner image transferred onto the recording paper is fixed by a fixing unit.
On the one hand, the toner left on the photoconductor after transfer is removed by a toner cleaner, and used for forming a new electrostatic latent image or toner image. In the image forming apparatus, a mechanism for efficiently removing toner and ejecting the removed toner to the outside is essential and important.
Accordingly, for example, as disclosed in Patent Document (JP 10-301460 A), various kinds of toner eject mechanisms have been conventionally proposed.
On the other hand, there are many image forming apparatuses of type that the toner image formed on the photoconductor is once transferred onto an intermediate transfer body such as an intermediate transfer belt, and the toner image transferred onto the intermediate transfer body is transferred onto recording paper. In the image forming apparatus of this type, since toner is left not only on the photoconductor but also on the intermediate transfer body, toner cleaners are often provided for both the photoconductor and the intermediate transfer body.
As a technology of cleaning toner attached to the photoconductor, intermediate transfer body, etc. (these are generally named as an image carrier), a technology of removing toner by pressing an elastic body of urethane rubber or the like molded in a blade shape (hereinafter, referred to as “cleaning blade”) against the image carrier has been generally used.
For example, the toner cleaner includes a cleaning blade formed by attaching a rubber material having a free length of specified length to a base such as a metal plate, transporting means for transporting the toner removed from the image carrier by the cleaning blade (hereinafter, referred as “waste toner”) to a predetermined position, a casing for accommodating the cleaning blade and the transporting means, etc.
As methods of pressing the cleaning blade against the image carrier, there are a fixed position method by which the cleaning blade is fixed to the casing fixed relative to the image carrier and a fixed weight method by which a specified weight is applied to the cleaning blade by pressurizing means such as a spring.
In the fixed position method, although the structure is relatively simple, the force of the cleaning blade pressing the image carrier (pressing force) varies widely due to the attachment error of the cleaning blade relative to the position of the image carrier, variations in dimension precision of the cleaning blade alone, change of the cleaning blade over time, environmental dependency of elasticity, etc., and the method has a disadvantage that the cleaning performance of the cleaning blade is unstable.
Contrary, pressing force varies little in the fixed weight method and the method can realize stable cleaning performance.
The fixed weight method is further classified into the following two methods. One has a form in which a holder having the cleaning blade, a rotational part, and an attachment part of the spring is rotatably supported by a casing and only the holder and the cleaning blade are moved relative to the image carrier. In this method, sealing with a sponge or the like is needed for preventing leak of toner from a gap between the cleaning blade and the casing, and there is a disadvantage that it is difficult to realize effective sealing because the seal moves relative to the casing.
The other method is a method of fixing the cleaning blade to the casing and pressurizing the entire casing including the transporting means of waste toner by the spring or the like for pressing the cleaning blade to the image carrier (hereinafter, referred to as “transportation integrated blade method”). In the transportation integrated blade method, the cleaning blade does not move relative to the casing, and the method has an advantage that the prevention of waste toner leaking from the casing becomes easier.
However, in the transportation integrated blade method, since the transporting means and the cleaning blade are fixed to the casing, there has been a problem that the variation in force received by the transporting means easily leads to the variation in pressing force of the cleaning blade, and consequently, the variation is likely to cause a phenomenon that the cleaning blade is flipped and degradation in cleaning performance of the cleaning blade.